On 12 Jan 2009, at 02:32, "Michael Ash" <michael....@gmail.com> wrote:
In thinking about memory usage, where previously I would think of
my program
in terms of 8 or 16 or 32 bit words should I now be thinking in
terms of 64
bit words?
That is, should I think of my available internal memory space as
effectively
being 500MB words?
No, this makes no sense. You have 2GB of memory. If you're working
with 64-bit words then it makes sense to think of your memory as being
roughly 256 million words (note: not 500) but that's not the same as
"500MB words".
Yes, of course. Silly mistake.
Similarly, say that I had 100MB of 2 x 8-bit byte integers to save
to disk,
should I now think that this will be saved as 100MB by 64 bit (i.e.
8 x
8-bit byte) integers?
If it is 100MB by 64 bit integers then should I think of
compressing the
data so as to reduce bandwidth requirements?
Just because your machine has a 64-bit processor doesn't mean you're
suddenly required to work with 64-bit quantities everywhere. You can
still work with 8, 16, or 32-bit quantities as you need.
Yes, but my understanding is that this will change when we go into a
full 64 bit architecture and as a one man band I would prefer to write
code that anticipates the change than to have to change everything
later.
Also, the documentation
http://tinyurl.com/6ceoqz
leads me to believe that if I need an address space of more than 4GB
then I should be using 64 bit computing.
Which one is
the most appropriate choice, I couldn't say, but you seem to have this
strange idea that your 8-bit integers will somehow magically take up
64 bits of storage just because you're running on a Core2
architecture. It's simply not the case.
I'm glad you've flagged this up because one of the reasons for my
asking the question was to increase my understanding of what I should
and should not be thinking about in this regard.
So let me then ask: under the 64 bit architecture, will the standard c
types like int, char etc still be available and not give me problems
under garbage collection given I define them as strong?
Currently I'm defining most my variables as type NSInteger and
CGFloat. Is that wrong?
Or should I be implementing my numbers as NSNumber? I thought the main
purpose of NSNumber was as a wrapper to enable us to put numbers into
NSArray etc. Would not using it as the main representation seriously
affect computation speed ? What are other people doing?
If you have any good links or advice they'd be much appreciated.
Thanks
Julius
http://juliuspaintings.co.uk
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